Probiotic yoghurt functionalised with microalgae and Zedo gum: chemical,microbiological, rheological and sensory characteristics

In this study, using a central composite design, the effects of addition of Spirulina platensis and Zedo gum to plain and probiotic yoghurt samples were investigated during storage. Lactobacillus paracasei proliferation was directly dependent on the addition of microalgae and was inversely affected by storage time. Probiotic samples containing S. platensis showed the highest antioxidative activity. Maximum stability was obtained at higher amounts of Zedo gum, while organoleptic and rheological attributes improved at 0.25% Zedo gum. Given the importance of probiotic viability, supplementation of probiotic yoghurt with Zedo gum/S. platensis may be consideredas a novel nutraceutical formulation.     

Population dynamics of Salmonella spp. and Shigella spp. in ready-to-eat Mediterranean vegetable salads

This study evaluated the behavior of Salmonella and Shigella (5–6 log CFU/g) in tomato–cucumber (TC) salad without additives (control), TC with 1.0% lemon juice and 0.5% salt, TC with 10% wt/wt tahini, coleslaw, and toum sauce at 4, 10, or 24°C for 5 days. At 4°C, both pathogens survived well in all salads, with a 0.2–1.6 log CFU/g reduction after 5 days (except for toum sauce with >3.5 log CFU/g reduction after 4 days). At 10°C, Salmonella in the different TC salads remained constant, whereas Shigella numbers significantly increased by 1.0–1.7 log CFU/g after 5 days. Yet, both pathogens significantly decreased by 1.2–1.4 log CFU/g in coleslaw after 5 days and by >3.5 log CFU/g in toum sauce after 3 days. At 24°C, Salmonella significantly increased in TC salad without additives by 1.4 log CFU/g after 5 days and were below the detection level in the other types of salad after 5 days. However, Shigella numbers significantly increased by 1.0 log CFU/g in TC with tahini, but they significantly declined by 1.9–2.9 log CFU/g in TC salads after 5 days, and the pathogen was not detected in coleslaw and toum sauce after 4 days.     

Antioxidant properties of various solvent extracts of potato peel,sugar beet pulp and sesame cake

BACKGROUND: Growing interest in the replacement of synthetic food antioxidants by natural ones has fostered research on vegetable sources and screening of raw materials to identify new antioxidants. The food‐processing industry generates substantial quantities of phenolic‐rich by‐products that could be valuable natural sources of antioxidants. In this study the antioxidant properties and total phenolic, flavonoid and flavonol contents of three industrial by‐products, sugar beet pulp, sesame cake and potato peel, extracted with various solvents were examined. Since different antioxidant compounds have different mechanisms of action, several methods were used to assess the antioxidant efficacy of extracts. RESULTS: Among the six solvents tested, methanol gave the highest extract yield of potato peel and sugar beet pulp, while diethyl ether gave the highest extract yield of sesame cake. Methanol exhibited the highest extraction ability for phenolic compounds, with total phenolics amounting to 2.91, 1.79 and 0.81 mg gallic acid equivalent g^?1 dry weight in potato peel, sugar beet pulp and sesame cake extracts respectively, and also showed the strongest antioxidant capacity in the three assays used. All three methods proved that potato peel extract had the highest antioxidant activity owing to its high content of phenolic compounds and flavonoids. CONCLUSION: On the basis of the results obtained, potato peel, sugar beet pulp and sesame cake extracts could serve as natural antioxidants owing to their significant antioxidant activity. Therefore they could be used as preservative ingredients in the food and/or pharmaceutical industries. Copyright © 2009 Society of Chemical Industry     

Inactivation kinetics of inoculated Escherichia coli O157:H7, Listeria monocytogenes and Salmonella Poona on whole cantaloupe by chlorine dioxide gas

The objectives of this study were to examine inactivation kinetics of inoculated Escherichia coli O157:H7, Listeria monocytogenes and Salmonella Poona inoculated onto whole cantaloupe and treated with ClO(2) gas at different concentrations (0.5, 1.0, 1.5, 3.0 and 5.0 mg l(-1)) for different times (0, 2.0, 4.0, 6.0, 8.0 and 10.0 min). The effect of ClO(2) gas on the quality and shelf life of whole cantaloupe was also evaluated during storage at 22 degrees C for 12 days. A 100 microl inoculation of each targeted organism was spotted onto the surface (5 cm(2)) of cantaloupe rind (approximately 8-9 log CFU 5 cm(-2)) separately, air dried (60 min), and then treated with ClO(2) gas at 22 degrees C and 90-95% relative humidity for 10 min. Surviving bacterial populations on cantaloupe surfaces were determined using a membrane transferring method with a non-selective medium followed by a selective medium. The inactivation kinetics of E. coli O157:H7, L. monocytogenes and S. Poona were determined using nonlinear kinetics (Weibull model). A 3 log CFU reduction of E. coli O157:H7, L. monocytogenes and S. Poona were achieved with 5.0 mg l(-1) ClO(2) gas for 5.5, 4.2 and 1.5 min, respectively. A 5l og CFU reduction of S. Poona was achieved with 5.0 and 3.0 mg l(-1) ClO(2) gas for 6 and 8 min, respectively. A 4.6 and 4.3 log reduction was achieved after treatment with 5.0 mg l(-1) ClO(2) gas at 10 min for E. coli O157:H7 and L. monocytogenes, respectively. Treatment with 5.0 mg l(-1) ClO(2) gas significantly (p<0.05) reduced the initial microflora (mesophilic bacteria, psychrotrophic bacteria, and yeasts and molds) on cantaloupe by more than 2 log CFU cm(-2) and kept them significantly (p<0.05) lower than the untreated control during storage at 22 degrees C for 12 days. Treatment with ClO(2) gas did not significantly (p>0.05) affect the color of whole cantaloupe and extended the shelf life to 9 days compared to 3 days for the untreated control, when stored at ambient temperature (22 degrees C).     

Emergence of Antibiotic Resistance in Listeria monocytogenes Isolated from Food Products: A Comprehensive Review

Listeria monocytogenes is an opportunistic pathogen that has been involved in several deadly illness outbreaks. Future outbreaks may be more difficult to manage because of the emergence of antibiotic resistance among L. monocytogenes strains isolated from food products. The present review summarizes the available evidence on the emergence of antibiotic resistance among L. monocytogenes strains isolated from food products and the possible ways this resistance has developed. Furthermore, the resistance of food L. monocytogenes isolates to antibiotics currently used in the treatment of human listeriosis such as penicillin, ampicillin, tetracycline, and gentamicin, has been documented. Acquisition of movable genetic elements is considered the major mechanism of antibiotic resistance development in L. monocytogenes. Efflux pumps have also been linked with resistance of L. monocytogenes to some antibiotics including fluoroquinolones. Some L. monocytogenes strains isolated from food products are intrinsically resistant to several antibiotics. However, factors in food processing chains and environments (from farm to table) including extensive or sub‐inhibitory antibiotics use, horizontal gene transfer, exposure to environmental stresses, biofilm formation, and presence of persister cells play crucial roles in the development of antibiotic resistance by L. monocytogenes.     

Initial-strain analysis of silo—material interaction

Modifications to a finite element program developed in a prior study were extended for an initial-strain analysis of horizontal bending moments and hoop tension developed during bisymmetrical eccentric discharge. The results obtained by the newly developed initial-strain method, by the prior study, and those required by ACI Standard 313-77, were compared for a circular concrete silo.Although a significant difference in bending moment was obtained by the initial-strain and linear analysis methods, the steel reinforcement required was nearly the same at the lower elevation. However, at the upper elevation, approximately 50% more reinforcement was required for the initial-strain analysis. The reinforcement required by ACI Standard 313-77 was comparable to that for the initial-strain method at the higher elevation, and greater for the lower elevation.     

Combined microwave and enzymatic treatments for ��-lactoglobulin and bovine whey proteins and their effect on the IgE immunoreactivity

Effect of combined microwave (MW) and enzymatic hydrolysis on the human immunoglobulin E (IgE)-binding properties of ??-lactoglobulin (??-lg) and other whey proteins (WP) was investigated. Separated ??-lg and full whey protein isolate (WPI) were hydrolyzed with trypsin, chymotrypsin, mixture of trypsin/chymotrypsin, and pepsin at three microwave power levels: 50?W during 1 and 5?min, 100 and 200?W during 1 and 3?min. The immunoreactivity of the obtained hydrolysates resulting from combined microwave protease treatment was assessed using sera of young patients allergic to bovine whey proteins. The application of microwave treatment at 200?W enhances the hydrolysis of ??-lg by pepsin in 3?min and decreases significantly its immunoreactivity. The extensive hydrolysis of the microwave-treated ??-lg and WPI with trypsin, chymotrypsin, and the mixture of trypsin with chymotrypsin did not have an impact on the IgE binding of the products obtained in all the studied conditions.     

Proteolytic degradation of ewe milk proteins during fermentation of yoghurts and storage

Yoghurts are mostly produced from cow milk and to a very limited extent from ewe milk. The evolution of caseins and whey proteins in ovine milk submitted to different thermal treatments (63 degrees C/30 min; 73 degrees C/15 min; 85 degrees C/10 min or 96 degrees C/5 min) was followed during fermentation of yoghurts and during their storage up to 14 days, using two different sets of starters. One set of starter LAB was a "ropy" culture (YC-191), which is a well-defined mixed strain culture containing Streptococcus thermophilus ST-143 and Lactobacillus delbrueckii subsp. bulgaricus (LB-18 and LB-CH2). The other set of starter bacteria (YC-460) was a standard yoghurt culture("non-ropy") containing mixed strain culture of Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus. Contents of free amino groups in produced yoghurts increased gradually during the fermentation, up to a maximal value obtained after 4 h fermentation, then they did not change significantly during storage of yoghurt produced with YC-191 starter. In contrary, a large drop in the amount of free amino groups was observed in the first 24 h of storage in the case of yoghurt made with YC-460 indicating that microorganisms continue still to grow in low temperatures. During fermentation and storage of both yoghurt types, alpha-lactalbumin was hydrolyzed to a slightly bigger extent than beta-lactoglobulin. During fermentation, beta-casein was slightly more degraded than alpha(s)-caseins; however, the opposite was observed during storage up to 14 days. Generally, a more intense heat pretreatment led to a higher degradation of whey proteins and caseins during fermentation and storage. Differences in proteolytic activity between the two starters used (whey proteins more degraded by YC-191; caseins more degraded by YC-460) may lead to improvement in production and formulation of yoghurts differing in their physicochemical and rheological properties.